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Linux/fs/timerfd.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  *  fs/timerfd.c
  4  *
  5  *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
  6  *
  7  *
  8  *  Thanks to Thomas Gleixner for code reviews and useful comments.
  9  *
 10  */
 11 
 12 #include <linux/alarmtimer.h>
 13 #include <linux/file.h>
 14 #include <linux/poll.h>
 15 #include <linux/init.h>
 16 #include <linux/fs.h>
 17 #include <linux/sched.h>
 18 #include <linux/kernel.h>
 19 #include <linux/slab.h>
 20 #include <linux/list.h>
 21 #include <linux/spinlock.h>
 22 #include <linux/time.h>
 23 #include <linux/hrtimer.h>
 24 #include <linux/anon_inodes.h>
 25 #include <linux/timerfd.h>
 26 #include <linux/syscalls.h>
 27 #include <linux/compat.h>
 28 #include <linux/rcupdate.h>
 29 
 30 struct timerfd_ctx {
 31         union {
 32                 struct hrtimer tmr;
 33                 struct alarm alarm;
 34         } t;
 35         ktime_t tintv;
 36         ktime_t moffs;
 37         wait_queue_head_t wqh;
 38         u64 ticks;
 39         int clockid;
 40         short unsigned expired;
 41         short unsigned settime_flags;   /* to show in fdinfo */
 42         struct rcu_head rcu;
 43         struct list_head clist;
 44         spinlock_t cancel_lock;
 45         bool might_cancel;
 46 };
 47 
 48 static LIST_HEAD(cancel_list);
 49 static DEFINE_SPINLOCK(cancel_lock);
 50 
 51 static inline bool isalarm(struct timerfd_ctx *ctx)
 52 {
 53         return ctx->clockid == CLOCK_REALTIME_ALARM ||
 54                 ctx->clockid == CLOCK_BOOTTIME_ALARM;
 55 }
 56 
 57 /*
 58  * This gets called when the timer event triggers. We set the "expired"
 59  * flag, but we do not re-arm the timer (in case it's necessary,
 60  * tintv != 0) until the timer is accessed.
 61  */
 62 static void timerfd_triggered(struct timerfd_ctx *ctx)
 63 {
 64         unsigned long flags;
 65 
 66         spin_lock_irqsave(&ctx->wqh.lock, flags);
 67         ctx->expired = 1;
 68         ctx->ticks++;
 69         wake_up_locked(&ctx->wqh);
 70         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
 71 }
 72 
 73 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
 74 {
 75         struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx,
 76                                                t.tmr);
 77         timerfd_triggered(ctx);
 78         return HRTIMER_NORESTART;
 79 }
 80 
 81 static enum alarmtimer_restart timerfd_alarmproc(struct alarm *alarm,
 82         ktime_t now)
 83 {
 84         struct timerfd_ctx *ctx = container_of(alarm, struct timerfd_ctx,
 85                                                t.alarm);
 86         timerfd_triggered(ctx);
 87         return ALARMTIMER_NORESTART;
 88 }
 89 
 90 /*
 91  * Called when the clock was set to cancel the timers in the cancel
 92  * list. This will wake up processes waiting on these timers. The
 93  * wake-up requires ctx->ticks to be non zero, therefore we increment
 94  * it before calling wake_up_locked().
 95  */
 96 void timerfd_clock_was_set(void)
 97 {
 98         ktime_t moffs = ktime_mono_to_real(0);
 99         struct timerfd_ctx *ctx;
100         unsigned long flags;
101 
102         rcu_read_lock();
103         list_for_each_entry_rcu(ctx, &cancel_list, clist) {
104                 if (!ctx->might_cancel)
105                         continue;
106                 spin_lock_irqsave(&ctx->wqh.lock, flags);
107                 if (ctx->moffs != moffs) {
108                         ctx->moffs = KTIME_MAX;
109                         ctx->ticks++;
110                         wake_up_locked(&ctx->wqh);
111                 }
112                 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
113         }
114         rcu_read_unlock();
115 }
116 
117 static void __timerfd_remove_cancel(struct timerfd_ctx *ctx)
118 {
119         if (ctx->might_cancel) {
120                 ctx->might_cancel = false;
121                 spin_lock(&cancel_lock);
122                 list_del_rcu(&ctx->clist);
123                 spin_unlock(&cancel_lock);
124         }
125 }
126 
127 static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
128 {
129         spin_lock(&ctx->cancel_lock);
130         __timerfd_remove_cancel(ctx);
131         spin_unlock(&ctx->cancel_lock);
132 }
133 
134 static bool timerfd_canceled(struct timerfd_ctx *ctx)
135 {
136         if (!ctx->might_cancel || ctx->moffs != KTIME_MAX)
137                 return false;
138         ctx->moffs = ktime_mono_to_real(0);
139         return true;
140 }
141 
142 static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
143 {
144         spin_lock(&ctx->cancel_lock);
145         if ((ctx->clockid == CLOCK_REALTIME ||
146              ctx->clockid == CLOCK_REALTIME_ALARM) &&
147             (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
148                 if (!ctx->might_cancel) {
149                         ctx->might_cancel = true;
150                         spin_lock(&cancel_lock);
151                         list_add_rcu(&ctx->clist, &cancel_list);
152                         spin_unlock(&cancel_lock);
153                 }
154         } else {
155                 __timerfd_remove_cancel(ctx);
156         }
157         spin_unlock(&ctx->cancel_lock);
158 }
159 
160 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
161 {
162         ktime_t remaining;
163 
164         if (isalarm(ctx))
165                 remaining = alarm_expires_remaining(&ctx->t.alarm);
166         else
167                 remaining = hrtimer_expires_remaining_adjusted(&ctx->t.tmr);
168 
169         return remaining < 0 ? 0: remaining;
170 }
171 
172 static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
173                          const struct itimerspec64 *ktmr)
174 {
175         enum hrtimer_mode htmode;
176         ktime_t texp;
177         int clockid = ctx->clockid;
178 
179         htmode = (flags & TFD_TIMER_ABSTIME) ?
180                 HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
181 
182         texp = timespec64_to_ktime(ktmr->it_value);
183         ctx->expired = 0;
184         ctx->ticks = 0;
185         ctx->tintv = timespec64_to_ktime(ktmr->it_interval);
186 
187         if (isalarm(ctx)) {
188                 alarm_init(&ctx->t.alarm,
189                            ctx->clockid == CLOCK_REALTIME_ALARM ?
190                            ALARM_REALTIME : ALARM_BOOTTIME,
191                            timerfd_alarmproc);
192         } else {
193                 hrtimer_init(&ctx->t.tmr, clockid, htmode);
194                 hrtimer_set_expires(&ctx->t.tmr, texp);
195                 ctx->t.tmr.function = timerfd_tmrproc;
196         }
197 
198         if (texp != 0) {
199                 if (isalarm(ctx)) {
200                         if (flags & TFD_TIMER_ABSTIME)
201                                 alarm_start(&ctx->t.alarm, texp);
202                         else
203                                 alarm_start_relative(&ctx->t.alarm, texp);
204                 } else {
205                         hrtimer_start(&ctx->t.tmr, texp, htmode);
206                 }
207 
208                 if (timerfd_canceled(ctx))
209                         return -ECANCELED;
210         }
211 
212         ctx->settime_flags = flags & TFD_SETTIME_FLAGS;
213         return 0;
214 }
215 
216 static int timerfd_release(struct inode *inode, struct file *file)
217 {
218         struct timerfd_ctx *ctx = file->private_data;
219 
220         timerfd_remove_cancel(ctx);
221 
222         if (isalarm(ctx))
223                 alarm_cancel(&ctx->t.alarm);
224         else
225                 hrtimer_cancel(&ctx->t.tmr);
226         kfree_rcu(ctx, rcu);
227         return 0;
228 }
229 
230 static __poll_t timerfd_poll(struct file *file, poll_table *wait)
231 {
232         struct timerfd_ctx *ctx = file->private_data;
233         __poll_t events = 0;
234         unsigned long flags;
235 
236         poll_wait(file, &ctx->wqh, wait);
237 
238         spin_lock_irqsave(&ctx->wqh.lock, flags);
239         if (ctx->ticks)
240                 events |= EPOLLIN;
241         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
242 
243         return events;
244 }
245 
246 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
247                             loff_t *ppos)
248 {
249         struct timerfd_ctx *ctx = file->private_data;
250         ssize_t res;
251         u64 ticks = 0;
252 
253         if (count < sizeof(ticks))
254                 return -EINVAL;
255         spin_lock_irq(&ctx->wqh.lock);
256         if (file->f_flags & O_NONBLOCK)
257                 res = -EAGAIN;
258         else
259                 res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
260 
261         /*
262          * If clock has changed, we do not care about the
263          * ticks and we do not rearm the timer. Userspace must
264          * reevaluate anyway.
265          */
266         if (timerfd_canceled(ctx)) {
267                 ctx->ticks = 0;
268                 ctx->expired = 0;
269                 res = -ECANCELED;
270         }
271 
272         if (ctx->ticks) {
273                 ticks = ctx->ticks;
274 
275                 if (ctx->expired && ctx->tintv) {
276                         /*
277                          * If tintv != 0, this is a periodic timer that
278                          * needs to be re-armed. We avoid doing it in the timer
279                          * callback to avoid DoS attacks specifying a very
280                          * short timer period.
281                          */
282                         if (isalarm(ctx)) {
283                                 ticks += alarm_forward_now(
284                                         &ctx->t.alarm, ctx->tintv) - 1;
285                                 alarm_restart(&ctx->t.alarm);
286                         } else {
287                                 ticks += hrtimer_forward_now(&ctx->t.tmr,
288                                                              ctx->tintv) - 1;
289                                 hrtimer_restart(&ctx->t.tmr);
290                         }
291                 }
292                 ctx->expired = 0;
293                 ctx->ticks = 0;
294         }
295         spin_unlock_irq(&ctx->wqh.lock);
296         if (ticks)
297                 res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
298         return res;
299 }
300 
301 #ifdef CONFIG_PROC_FS
302 static void timerfd_show(struct seq_file *m, struct file *file)
303 {
304         struct timerfd_ctx *ctx = file->private_data;
305         struct itimerspec t;
306 
307         spin_lock_irq(&ctx->wqh.lock);
308         t.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
309         t.it_interval = ktime_to_timespec(ctx->tintv);
310         spin_unlock_irq(&ctx->wqh.lock);
311 
312         seq_printf(m,
313                    "clockid: %d\n"
314                    "ticks: %llu\n"
315                    "settime flags: 0%o\n"
316                    "it_value: (%llu, %llu)\n"
317                    "it_interval: (%llu, %llu)\n",
318                    ctx->clockid,
319                    (unsigned long long)ctx->ticks,
320                    ctx->settime_flags,
321                    (unsigned long long)t.it_value.tv_sec,
322                    (unsigned long long)t.it_value.tv_nsec,
323                    (unsigned long long)t.it_interval.tv_sec,
324                    (unsigned long long)t.it_interval.tv_nsec);
325 }
326 #else
327 #define timerfd_show NULL
328 #endif
329 
330 #ifdef CONFIG_CHECKPOINT_RESTORE
331 static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
332 {
333         struct timerfd_ctx *ctx = file->private_data;
334         int ret = 0;
335 
336         switch (cmd) {
337         case TFD_IOC_SET_TICKS: {
338                 u64 ticks;
339 
340                 if (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
341                         return -EFAULT;
342                 if (!ticks)
343                         return -EINVAL;
344 
345                 spin_lock_irq(&ctx->wqh.lock);
346                 if (!timerfd_canceled(ctx)) {
347                         ctx->ticks = ticks;
348                         wake_up_locked(&ctx->wqh);
349                 } else
350                         ret = -ECANCELED;
351                 spin_unlock_irq(&ctx->wqh.lock);
352                 break;
353         }
354         default:
355                 ret = -ENOTTY;
356                 break;
357         }
358 
359         return ret;
360 }
361 #else
362 #define timerfd_ioctl NULL
363 #endif
364 
365 static const struct file_operations timerfd_fops = {
366         .release        = timerfd_release,
367         .poll           = timerfd_poll,
368         .read           = timerfd_read,
369         .llseek         = noop_llseek,
370         .show_fdinfo    = timerfd_show,
371         .unlocked_ioctl = timerfd_ioctl,
372 };
373 
374 static int timerfd_fget(int fd, struct fd *p)
375 {
376         struct fd f = fdget(fd);
377         if (!f.file)
378                 return -EBADF;
379         if (f.file->f_op != &timerfd_fops) {
380                 fdput(f);
381                 return -EINVAL;
382         }
383         *p = f;
384         return 0;
385 }
386 
387 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
388 {
389         int ufd;
390         struct timerfd_ctx *ctx;
391 
392         /* Check the TFD_* constants for consistency.  */
393         BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
394         BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
395 
396         if ((flags & ~TFD_CREATE_FLAGS) ||
397             (clockid != CLOCK_MONOTONIC &&
398              clockid != CLOCK_REALTIME &&
399              clockid != CLOCK_REALTIME_ALARM &&
400              clockid != CLOCK_BOOTTIME &&
401              clockid != CLOCK_BOOTTIME_ALARM))
402                 return -EINVAL;
403 
404         if ((clockid == CLOCK_REALTIME_ALARM ||
405              clockid == CLOCK_BOOTTIME_ALARM) &&
406             !capable(CAP_WAKE_ALARM))
407                 return -EPERM;
408 
409         ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
410         if (!ctx)
411                 return -ENOMEM;
412 
413         init_waitqueue_head(&ctx->wqh);
414         spin_lock_init(&ctx->cancel_lock);
415         ctx->clockid = clockid;
416 
417         if (isalarm(ctx))
418                 alarm_init(&ctx->t.alarm,
419                            ctx->clockid == CLOCK_REALTIME_ALARM ?
420                            ALARM_REALTIME : ALARM_BOOTTIME,
421                            timerfd_alarmproc);
422         else
423                 hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
424 
425         ctx->moffs = ktime_mono_to_real(0);
426 
427         ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
428                                O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
429         if (ufd < 0)
430                 kfree(ctx);
431 
432         return ufd;
433 }
434 
435 static int do_timerfd_settime(int ufd, int flags, 
436                 const struct itimerspec64 *new,
437                 struct itimerspec64 *old)
438 {
439         struct fd f;
440         struct timerfd_ctx *ctx;
441         int ret;
442 
443         if ((flags & ~TFD_SETTIME_FLAGS) ||
444                  !itimerspec64_valid(new))
445                 return -EINVAL;
446 
447         ret = timerfd_fget(ufd, &f);
448         if (ret)
449                 return ret;
450         ctx = f.file->private_data;
451 
452         if (isalarm(ctx) && !capable(CAP_WAKE_ALARM)) {
453                 fdput(f);
454                 return -EPERM;
455         }
456 
457         timerfd_setup_cancel(ctx, flags);
458 
459         /*
460          * We need to stop the existing timer before reprogramming
461          * it to the new values.
462          */
463         for (;;) {
464                 spin_lock_irq(&ctx->wqh.lock);
465 
466                 if (isalarm(ctx)) {
467                         if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
468                                 break;
469                 } else {
470                         if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
471                                 break;
472                 }
473                 spin_unlock_irq(&ctx->wqh.lock);
474                 cpu_relax();
475         }
476 
477         /*
478          * If the timer is expired and it's periodic, we need to advance it
479          * because the caller may want to know the previous expiration time.
480          * We do not update "ticks" and "expired" since the timer will be
481          * re-programmed again in the following timerfd_setup() call.
482          */
483         if (ctx->expired && ctx->tintv) {
484                 if (isalarm(ctx))
485                         alarm_forward_now(&ctx->t.alarm, ctx->tintv);
486                 else
487                         hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
488         }
489 
490         old->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
491         old->it_interval = ktime_to_timespec64(ctx->tintv);
492 
493         /*
494          * Re-program the timer to the new value ...
495          */
496         ret = timerfd_setup(ctx, flags, new);
497 
498         spin_unlock_irq(&ctx->wqh.lock);
499         fdput(f);
500         return ret;
501 }
502 
503 static int do_timerfd_gettime(int ufd, struct itimerspec64 *t)
504 {
505         struct fd f;
506         struct timerfd_ctx *ctx;
507         int ret = timerfd_fget(ufd, &f);
508         if (ret)
509                 return ret;
510         ctx = f.file->private_data;
511 
512         spin_lock_irq(&ctx->wqh.lock);
513         if (ctx->expired && ctx->tintv) {
514                 ctx->expired = 0;
515 
516                 if (isalarm(ctx)) {
517                         ctx->ticks +=
518                                 alarm_forward_now(
519                                         &ctx->t.alarm, ctx->tintv) - 1;
520                         alarm_restart(&ctx->t.alarm);
521                 } else {
522                         ctx->ticks +=
523                                 hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
524                                 - 1;
525                         hrtimer_restart(&ctx->t.tmr);
526                 }
527         }
528         t->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
529         t->it_interval = ktime_to_timespec64(ctx->tintv);
530         spin_unlock_irq(&ctx->wqh.lock);
531         fdput(f);
532         return 0;
533 }
534 
535 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
536                 const struct itimerspec __user *, utmr,
537                 struct itimerspec __user *, otmr)
538 {
539         struct itimerspec64 new, old;
540         int ret;
541 
542         if (get_itimerspec64(&new, utmr))
543                 return -EFAULT;
544         ret = do_timerfd_settime(ufd, flags, &new, &old);
545         if (ret)
546                 return ret;
547         if (otmr && put_itimerspec64(&old, otmr))
548                 return -EFAULT;
549 
550         return ret;
551 }
552 
553 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
554 {
555         struct itimerspec64 kotmr;
556         int ret = do_timerfd_gettime(ufd, &kotmr);
557         if (ret)
558                 return ret;
559         return put_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
560 }
561 
562 #ifdef CONFIG_COMPAT
563 COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
564                 const struct compat_itimerspec __user *, utmr,
565                 struct compat_itimerspec __user *, otmr)
566 {
567         struct itimerspec64 new, old;
568         int ret;
569 
570         if (get_compat_itimerspec64(&new, utmr))
571                 return -EFAULT;
572         ret = do_timerfd_settime(ufd, flags, &new, &old);
573         if (ret)
574                 return ret;
575         if (otmr && put_compat_itimerspec64(&old, otmr))
576                 return -EFAULT;
577         return ret;
578 }
579 
580 COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
581                 struct compat_itimerspec __user *, otmr)
582 {
583         struct itimerspec64 kotmr;
584         int ret = do_timerfd_gettime(ufd, &kotmr);
585         if (ret)
586                 return ret;
587         return put_compat_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
588 }
589 #endif
590 

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